The present invention concerns a process for the filling of tube electrodes for electrical accumulator batteries. More particularly, the process concerns wet filling of tube electrodes in which the active material is mixed with water and other liquids to form a paste. The process of the present invention is designed especially for use in connection with the production of positive tube electrodes for lead accumulator batteries. Electrodes for lead accumulator batteries and other conventional accumulator types are constructed around a frame or plate, the so-called grid, of electrically-conducting material which is wholly or partly surrounded by active material consisting of a porous structure of a metal or an organo-metallic compound. In lead electrodes the grid consists of a suitable lead-base alloy, and the active material of the positive electrode consists of lead oxides, primarily lead dioxide, when charged and of lead sulfate when discharged.
The positive electrodes are suitably produced as tube electrodes. Each such electrode comprises a number (generally 15 to 20) of tubes. Each tube, which often has a diameter of 5-10 mm, consists of an electrolytically pervious, resistant material, e.g., glass fiber. In the center of each tube there is a bar, i.e., a rod of suitable lead-base alloy, surrounded by active material which is held fast by the tube sheath. At this lower end the tubes are jointly compacted with the help of a so-called bottom strip and at the top with the help of an upper border, which consists of the same alloy as the rods and is electrically connected with the latter.
In the production of positive lead electrodes, a grid comprising the rods and upper border is first cast. The tube sheaths are drawn onto this grid, whereupon the active material is supplied conventionally in the form of dry powder, consisting chiefly of lead oxide. In order to obtain a complete filling and a consolidation of the active material, the electrodes are vibrated during the filling process.
The handling of the dry powder and especially the vibration causes the formation of a considerable amount of dust including lead dust. Because of the poisonous quality of the material, this leads to great inconvenience in connection with the filling of the electrodes. The loss of material, moreover, becomes unnecessarily great. In order to avoid these inconveniences to some degree, it has been suggested to use centrifugation instead of vibration. In this way, vibrating is avoided, but the disadvantages in connection with the handling of a dry powder remain. Special measures must also be taken in order to safeguard the powder delivery in connection with the centrifugation, and it has been suggested that the supply arrangements be worked out in such a way that the lead oxide dust be conveyed to the electrodes from a fluidized bed.
In order to avoid the disadvantages connected with the handling of the powder, several wet-filled methods have been suggested. The common feature of these methods is that the completely mixed paste of active material and water is pressed into the electrodes under high pressure. In order to overcome the pressure drop in the relatively long and narrow tubes, high pressure is required. Usually, a certain amount of surplus liquid is added in order to reduce the viscosity of the paste. The surplus liquid, which must flow out through the tube walls during application of the high pressure, carries along a not insignificant amount of small lead particles. There are several undesirable consequences: a size fractionation of the material, a considerable dirtying of the outer side of the electrodes, and problems in connection with the managing of the lead-contaminated waste water. To avoid these problems it has been suggested to impregnate the tube sheaths with a sealing or proofing compound before filling. The sealing compound selected should be soluble in water or sulfuric acid and is removed by washing of the electrodes after filling. However, this requires a reduction of the liquid addition to the paste, which makes necessary an even greater pressure for the introduction of the paste in the electrodes.